Blender Git Loki

Fix for bug [#21534] Multires modifier strange deformations

This adds the "Apply Base" feature from my gsoc2010 branch.

Apply Base partially applies the modifier, in that the mesh is
reshaped to more closely match the deformed mesh. The upper-level
displacements are recalculated so that the highest multires level
appears unchanged.

Multires does not currently deal well with too large displacements.
An easy-to-reproduce example: create any mesh type, add multires,
subdivide a few times, then use the sculpt grab brush to drag the
entire mesh over a few units. At the highest level, and at level 0,
the mesh looks fine, but all of the intervening levels will have ugly
spikes on them.

This patch doesn't help with situations where you can't modify the
base mesh, but otherwise works around the problem fairly well (albeit
with a heuristic, not an exact solution.)